ControlMode(test[regressions]): Add missing repros from full control suite

why: Cover every failing control-mode case observed in full pytest run.
what:
- Add capture-pane variant repros (default/start/end) and integration prompt check
- Add environment propagation repros for new-window and split-window
- Add attached_sessions visibility check and server.kill EOF repro
- Keep xfail strict markers for all known control-mode discrepancies

Author: tony

tests/test_control_mode_regressions.py

@@ -302,6 +302,89 @@ def test_attached_sessions_empty_when_no_clients() -> None:
             server.kill()
 
 
+class CapturePaneFixture(t.NamedTuple):
+    """Fixture for capture-pane variants that should trim blanks."""
+
+    test_id: str
+    start: t.Literal["-"] | int | None
+    end: t.Literal["-"] | int | None
+    expected: str
+
+
+CAPTURE_PANE_CASES = [
+    pytest.param(
+        CapturePaneFixture(
+            test_id="default",
+            start=None,
+            end=None,
+            expected="$",
+        ),
+        id="capture_default",
+        marks=pytest.mark.xfail(
+            reason="control-mode capture-pane returns extra blank lines",
+            strict=True,
+        ),
+    ),
+    pytest.param(
+        CapturePaneFixture(
+            test_id="start_history",
+            start=-2,
+            end=None,
+            expected='$ printf "%s"\n$ clear -x\n$',
+        ),
+        id="capture_start",
+        marks=pytest.mark.xfail(
+            reason="control-mode capture-pane start preserves trailing blanks",
+            strict=True,
+        ),
+    ),
+    pytest.param(
+        CapturePaneFixture(
+            test_id="end_zero",
+            start=None,
+            end=0,
+            expected='$ printf "%s"',
+        ),
+        id="capture_end_zero",
+        marks=pytest.mark.xfail(
+            reason="control-mode capture-pane end preserves trailing blanks",
+            strict=True,
+        ),
+    ),
+]
+
+
+@pytest.mark.parametrize("case", CAPTURE_PANE_CASES)
+def test_capture_pane_variants(case: CapturePaneFixture) -> None:
+    """capture-pane variants should return trimmed output like subprocess engine."""
+    env = shutil.which("env")
+    assert env is not None
+
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        session = server.new_session(
+            session_name=f"capture_variant_{case.test_id}",
+            attach=True,
+            window_shell=f"{env} PS1='$ ' sh",
+            kill_session=True,
+        )
+        pane = session.active_window.active_pane
+        assert pane is not None
+
+        pane.send_keys(r'printf "%s"', literal=True, suppress_history=False)
+        pane.send_keys("clear -x", literal=True, suppress_history=False)
+
+        output_lines = pane.capture_pane(start=case.start, end=case.end)
+        output = "\n".join(output_lines)
+        assert output == case.expected
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()
+
+
 @pytest.mark.xfail(
     reason="control-mode is_alive bootstrap hides missing-server errors",
     strict=True,
@@ -329,3 +412,34 @@ def test_testserver_is_alive_false_before_use() -> None:
     finally:
         with contextlib.suppress(Exception):
             server.kill()
+
+
+@pytest.mark.xfail(
+    reason=(
+        "server.kill with control engine can raise ControlModeConnectionError on EOF"
+    ),
+    strict=True,
+)
+def test_server_kill_handles_control_eof_gracefully() -> None:
+    """server.kill should not propagate ControlModeConnectionError after tmux exits."""
+    socket_name = f"libtmux_test_{uuid.uuid4().hex[:8]}"
+    engine = ControlModeEngine()
+    server = Server(socket_name=socket_name, engine=engine)
+
+    try:
+        session = server.new_session(
+            session_name="kill_eof_repro",
+            attach=False,
+            kill_session=True,
+        )
+        assert session is not None
+        # Simulate tmux disappearing before control client issues kill-server.
+        subprocess.run(
+            ["tmux", "-L", socket_name, "kill-server"],
+            check=False,
+            capture_output=True,
+        )
+        server.kill()
+    finally:
+        with contextlib.suppress(Exception):
+            server.kill()